5.1.5 Plant and Animal Responses Flashcards
What is abiotic stress ?
•Non-living environmental factor that could harm a plant
•Examples include mineral deficiency, drought, depleted oxygen supply.
How do plants respond to abiotic stress and herbivory ?
•Producing antifreeze enzymes
•Producing bitter tasting tannins and alkaloids
•Produce pheromones to induce a response in other organisms
What is a plant tropism ?
•Directional growth in response to a stimulus in plants, examples include :
->Phototropism (light)
->Geotropism (gravity)
->Hydrotropism (water)
->Thermotropism (temperature)
->Thigmotropism (touching a surface).
How is leaf loss in deciduous plants controlled ?
•As leaf ages cytokinin and auxin levels lower, ethene level rises
•This triggers the production of cellulase enzymes which weaken leaves by breaking down cell wall
•Leaves then break from the branch.
List the function of gibberellins
They stimulate :
•Germination
•Elongation at cell internodes
•Fruit growth
•Rapid growth / flowering.
How is germination stimulated ?
•Seed absorbs water to stimulate secretion of gibberellins
•Gibberellins stimulate production of amylase
•Amylase hydrolyses starch
•The products is sugar which is respired to produce ATP.
List the functions of auxins
•Involved in trophic responses
•Control cell elongation
•Suppress lateral buds to maintain apical dominance
•Promote root growth.
Explain how shoots show positive phototropism
•IAA diffuses to shaded part of tip
•As IAA diffuses down the shaded side, it causes the active transport of H+ ions into the cell walls
•The causes the disruption of H-bonds between molecules and causes expansins to make the wall more permeable to water
•This causes cells on the shaded side to elongate faster
•Shoot grows towards the light.
Explain why shoots show positive geotropism
•Gravity causes IAA to accumulate on the lower side of the roots
•IAA inhibits the elongation of root cells
•Cells on upper side grow faster and roots bend downward.
How do hormones stimulate the stomata to close ?
•Asbestic acid binds to complementary receptors on guard cell membrane, opening Ca2+ ion channel and allow Ca2+ out
• Positive feedback means more Ca2+ channels open, other ions diffuse out
•Water potential of cells become more positive and water diffuses out via osmosis
•Guard cells become flaccid so stomata close.
What is apical dominance ?
•When the shoot grows, the side shoots do not grow with priority
•Maintained by auxins, asbestic acid and cytokinins.
Explain the experimental evidence that auxins maintain apical dominance
Auxin production in tip maintains high levels of abscisic acid, this inhibits the growth of side shoots
Explain the evidence that gibberellins control stem elongation and germination
•Stem elongation: Tall plants have higher gibberellin concentrations than dwarf plants
•Germination: Mutant seeds with non-functional gibberellin gene do not germinate unless gibberellin is applied.
How are auxins used commercially ?
Auxins: rooting powder, growing seedless fruit (low conc prevent leaf and fruit growth, high conc promote fruit drop)
How are cytokinins used commercially ?
Preventing yellowing of leaves such as lettuce, promotes shoot growth.
